This invention relates to a length-adjusting device for use with a gas spring, and more particularly to a length-adjusting device which is capable of adjusting length accurately by operating an operating lever directly coupled to the gas spring.
A length-adjusting device for use with a gas spring which serves as a support of a chair is known and adjusts the height of a seat of the chair to any desired position in non-step fashion.
As is known to those skilled in the art, gas springs are classified into a single cylinder type and a double-cylinder type having inner and outer cylinders. The construction of the double-cylinder type gas spring of the prior art is as described below.
An inner cavity defined by an inner cylinder and an outer cavity defined by the inner cylinder and outer cylinder are communicated with each other by way of communicating means which are provided in the top and bottom portions or at the left and right ends, and a length-adjusting valve is provided in one of said communicating means, so as to open and close the latter. The gas spring is filled with high pressure gas and liquid, while a rod integral with a piston adapted to slide within the inner cavity, and the outer periphery of the outer cylinder are attached to a stationary member and a movable member, or to a movable member and a stationary member, respectively. If the length-adjusting valve is maintained closed, no movement of liquid within respective cavities through the communicating means takes place, thereby holding the movable member in place. When the valve is open, the gas is free to move, thereby permitting the movable member to shift to a desired position.
On the other hand, in the single cylinder type gas spring, gas and liquid are both charged in a single cylinder, and a piston having a rod projecting from the cylinder is inserted in the oil portion. A partition wall is provided in the oil portion so as not to interfere with the sliding motion of the piston, so that the oil portion is vertically partitioned into a liquid chamber in which the piston is inserted, and a gas chamber. The partition wall is provided with a passage so these upper and lower chambers are in communication with each other, and has a length-adjusting valve for opening and closing the passage, so as to adjust the length of the gas spring.
An example of a known gas spring applied to a chair for adjusting the height of the seat is shown in FIG. 1 for reference purposes. As is obvious from FIG. 1, it has been a common practice that a lever for operating a length-or height-adjusting valve 5 is pivotally mounted on a bracket 3 which is rigidly secured beforehand by, for example, welding to a seat-supporting member 2 of a seat 1, because of ease of assembly. Because of the construction described, the gas spring shown as a known example has many drawbacks in that, upon assembly of a hydraulic spring 7 to the seat 1, there is left excessive clearance at a contacting point 6 between the operating lever 4 and the height-adjusting valve 5 of the spring, or both members are positioned too closely to each other, thus causing jamming in an adjusting operation, or there incurs an error to a greater extent to the stroke of an operating lever. In addition, when the case comes to the worst condition, an intended operation can not be achieved. The use of a welding process as means for fixing the bracket 3 to the seat-backing member 2 of the seat 1 incurs an increased manufacturing cost. In order to eliminate any error in assembly, respective parts particularly the bracket must be disposed in position with high accuracy.